Solvent flux behaviour and rejection characteristics of hydrophilic and hydrophobic TiO2 and ZrO2 membranes

Transcription

1 Solvent flux behaviour and rejection characteristics of hydrophilic and hydrophobic TiO2 and ZrO2 membranes Dobrak A.1, Verrecht B.1,2, Van den Dungen H.1, Leysen R.2, Buekenhoudt A.2, Van der Bruggen B1. 1Applied Physical Chemistry and Environmental Technology Section, KULeuven, Belgium 2Environmental and Process Technology, VITO, Mol, Belgium

2 Introduction: Outline - SRNF alternative?????? - Membranes which are suitable for a detailed transport description???? Materials and methods: - Set up, solvents, membranes, procedure Results and discussion solvent flux and rejection characteristics through ceramic membranes Conclusions: transport mechanism (viscous flow??) and rejection...

3 Introduction Solvent Resistant Nanofiltration (SRNF) = viable alternative for energy consuming conventional processes (distillation, evaporation...) New SRNF membranes: - Polymeric: swell and crack in non polar organic solvents - Ceramic: better chemical, thermal and mechanical resistance!!!

4 Materials and methods Experimental set up: cross flow filtration unit Membranes: - Hydrophilic TiO 2 (MWCO: 275, 650, 1400 and 7000 Da) manufactured by VITO (Mol, Belgium) and HITK (Hermsdorf, Germany) - Hydrophobic ZrO 2 (MWCO: 600 Da) manufactured by HITK (Hermsdorf, Germany) Solvents: water, methanol, ethanol, 2-propanol, toluene, n-hexane selected by molecular size, viscosity and polarity

5 Materials and methods Solvent flux measurements - Pressure: 5 bar for 275, 1400 Da TiO 2 and 600 Da ZrO 2 membranes 3 bar in case of 7000 Da TiO 2 membrane - Temperature range: C Rejection measurements - polyethyleneglycols (PEGs) + water - brilliant blue (MW=826 Da) + solvent (ethanol) - bromothymol blue (MW=624 Da) + solvents (ethanol, toluene)

6 Materials and methods Brilliant blue (MW = 826 Da) polar Bromothymol blue (MW = 624 Da) non-polar

7 Results: Hydrophilic TiO 2 membranes MWCO: 275 Da MWCO: 1400 Da 0,03 water 0,06 water 0,025 methanol 0,05 methanol Lp*η 0,02 0,015 0,01 0, T [ C] ethanol 2 - propanol n - hexane toluene Lp*η 0,04 0,03 0,02 0, T [ C] ethanol 2 - propanol n - hexane toluene No pure viscous flow

8 Results: Hydrophilic TiO 2 membranes MWCO: 275 Da MWCO: 1400 Da 0,03 water 0,06 water Lp*η 0,025 0,02 0,015 0,01 0, T [ C] methanol ethanol 2 - propanol n - hexane toluene Lp*η 0,05 0,04 0,03 0,02 0, T [ C] methanol ethanol 2 - propanol n - hexane toluene MWCO: 7000 Da Lp*η 0,05 0,04 0,03 0,02 0,01 0 toluene methanol 2 - propanol n - hexane ethanol water Viscous flow T [ C]

9 Results: Hydrophilic TiO 2 membranes Detailed temperature influenece on solvent flux MWCO: 275 Da J [l h -1 m -2 ] T [ C] methanol ethanol 2-propanol n-hexane toluene Increase of the flux values with about 100% from 20 to 50 C

10 Results: Observed activation energy MWCO [Da] Solvent E J [kj/mol] E η [kj/mol] E [kj/mol] 275 Water Methanol propanol Toluene n-hexane Water Methanol propanol Toluene n-hexane Water Methanol propanol Toluene n-hexane

11 Results: Hydrophobic ZrO 2 membrane 0,03 MWCO: 600 Da MWCO [Da] Solvent E J [kj/mol] E η [kj/mol] E [kj/mol] Lp*η 0,025 0,02 0,015 0,01 0,005 methanol ethanol 2-propanol n-hexane toluene Methanol T [ C] propanol Toluene Viscous flow n hexane

12 Results: Rejection characteristics Membrane MWCO Solute Solvent Rejection [%] Flux [l h -1 m -2 ] 25 C 50 C 25 C 50 C TiO Brilliant blue Bromothymol blue Toluene TiO Brilliant blue Bromothymol blue Toluene 55.5 \ \ ZrO Brilliant blue Bromothymol blue Toluene

13 Conclusions: Solvent flux Hydrophilic TiO 2 membranes - 275, 1400 Da permeability and viscosity increased with temperature Da the permeation mechanism of solvents obeys the viscous flow - Observed activation energies of solvent permeation were larger for membranes with lower MWCO and higher than the activation energies of solvent viscosity Hydrophobic ZrO 2 membranes - Increase of the flux with the temperature attributed to a viscosity decrease - Applicable for non-polar organic solvents (high n-hexane and toluene fluxes)

14 Conclusions: Rejection characteristics Temperature does not affect the rejections High values for hydrophilic membranes and low for hydrophobic membranes Polar brilliant blue rejections in ethanol were the highest (high molecular size of solute, affinity to the membrane surface...) Rejection of bromothymol blue (non-polar) was lower in ethanol (more polar) than in the toluene (less polar)!?

15 Acknowledgements K.U.Leuven Research Council (OT/06/37) VITO (PhD grant for B.Verrecht) For financial support!!!!